Silicon Nanoparticles: Excitonic Fine Structure and Oscillator Strength Cedrik Meier 1 , Stephan Lüttjohann 1 , Matthias Offer 1 , Hartmut Wiggers 2 , and Axel Lorke 1 1 Department of Physics and CeNIDE, University of Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany cedrik.meier@uni-due.de 2 Combustion & Gas Dynamics and CeNIDE, University of Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany Abstract. In this review, recent results on optical spectroscopy on silicon nanopar- ticles are summarized. We will demonstrate the quantum size effect observed in the photoluminescence for nanoparticles with diameters below 10 nm. Moreover, the ex- citonic fine structure splitting caused by the exchange interaction is investigated us- ing time-resolved and magnetic-field-dependent photoluminescence measurements. From these results, it is possible to estimate the rate of non-radiative recombina- tions in these nanoparticles, which allows to determine the oscillator strength and the quantum yield independently. 1 Introduction Silicon has in the past been the most important material for modern micro- electronics. In the last two decades, however, interest in nanostructured silicon has increased significantly. This development is on the one hand triggered by the ongoing miniaturization of silicon based integrated circuits for electronic applications, where critical dimensions CD < 100 nm can be reached in large scale production processes. On the other hand, the finding of photolumines- cence in porous silicon [1] has sparked the hope for silicon as a material also for optoelectronic applications. Until today, photoluminescence from nanos- tructured silicon could be demonstrated not only from porous silicon, but also silicon nanocrystals formed in an SiO 2 matrix by implantation of Si ions and subsequent annealing [2–4] and isolated silicon nanoparticles [5–8]. Re- cently, in silicon nanocrystal based devices amplified stimulated emission [9] and field-injection based electroluminescence [10] could be demonstrated. As an important prerequesite for optoelectronic device applications, one needs to have detailed knowledge of the recombination dynamics. In the case of silicon nanoparticles, this is of special importance, as bulk silicon is an indirect